TECHNICAL INDICES USED IN
GFP LAKE SURVEY REPORTS

Catch Per Unit Effort (CPUE) is the catch of animals in numbers or in weight taken by a defined period of effort. Can refer to trap-net nights of effort, gill-net nights of effort, catch per hour of electrofishing, etc.

Proportional Stock Density (PSD) is calculated by the following formula:

PSD = Number of fish > quality length x 100

Number of fish > stock length

Relative Stock Density (RSD-P) is calculated by the following formula:

RSD-P = Number of fish > preferred length x 100

Number of fish > stock length

PSD and RSD-P are unitless and usually calculated to the nearest whole digit.

Size categories for selected species found in Region 3 lake surveys, in centimeters.

PSD values within the target range indicate a balanced population. Values less than the target range indicate a population dominated by small fish and values greater than the target range indicate a population comprised mainly of large fish.

Relative weight (Wr) is a condition index that quantifies fish condition (i.e., how much does a fish weigh for its length). When mean Wr values are well below 100 for a size group, problems exist in food and feeding relationships. When mean Wr values are well above 100 for a size group, fish may not be making the best use of available prey.